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Unfortunately, property is not considered abandoned for a year or so. And then you need to show proof that you have given the owner written Notice to retrieve it.
You can write him a letter and explain that you are in no way responsible if his belongings are stolen and urge him to remove it before something should happen
A text would not hold up in court. Only a written letter. And, of course, you may sue him in small claims for the money he owes you. If the belongings are stolen you would not be responsible for a theft